As a technology studied by the inventors of the present invention, for example, the following technologies are known in the field of an electron microscope application apparatus and a sample inspection method.
Currently, in a manufacturing line for silicon devices, it is essential to inspect a wafer during a manufacturing process. This is because the inspection of a wafer during the manufacturing process can find the defect in an early stage and obtain the information for specifying a process causing the defect. By feeding back the inspection results to process conditions, the number of defects can be reduced, the number of chips obtained from one wafer can be increased, and yield can be improved.
As an apparatus for inspecting a wafer to find defects in the wafer, an optical inspection apparatus and an electron beam inspection apparatus are principally used. The optical inspection apparatus is an optical microscope in principle and can find shape defects such as particles and pattern defects. However, minute shape defects and electrical defects which cannot be detected by the optical inspection apparatus have become problems due to the development in finer design rule. Therefore, attention has been paid to an electron beam inspection apparatus which can detect the defects which cannot be detected by the optical inspection apparatus, and the electron beam inspection apparatus has been developed in several makers.
The detection of electrical defect in a silicon device by using the electron beam inspection apparatus is performed by charging a circuit pattern formed on a wafer surface and inspecting the contrast elicited by the charging. This process is called “voltage contrast method”, which is effective means for detecting electrical defect in a silicon device. In order to perform the inspection using the voltage contrast method with excellent reproducibility and high precision, it is necessary to control the charges of a circuit pattern to be inspected at high precision, and the improvement in control precision is directly linked to the improvement in detection precision for electrical defect.
As a method for controlling the charges of a wafer surface, a method based on electron beam irradiation and a method based on ultraviolet light irradiation have been disclosed (for example, Japanese Unexamined Patent Publication No. 2002-524827 (Patent Document 1) and Japanese Patent Application Laid-Open Publication No. 11-121561 (Patent Document 2)). In both the methods, electron beam or ultraviolet light is irradiated onto an area larger than an area observed in the case of using an electron beam inspection apparatus and the charges are made uniform.
Also, a method for removing the charges generated by the electron beam observation has been disclosed (for example, Japanese Patent Application Laid-Open Publication No. 2004-363085 (Patent Document 3)). In the Patent Document 3, charges of a sample are removed or made uniform by irradiating ultraviolet light onto metal so as to irradiate photoelectrons emitted by photoelectric effect onto the sample instead of directly irradiating ultraviolet light onto the sample.